The present invention relates in general to power supplies for electrical circuits implemented upon printed circuit boards and, in particular, to an electrical ground plane apparatus which provides for direct coupling of analog and digital circuitry, while substantially minimizing the injection of RF noise into circuits operably connected to the protected circuit board.
The problems associated with placing analog and digital circuitry onto the same circuit board are well known in the art. The most significant problems arise from the high RF noise produced by digital circuits which typically interferes with sensitive, noise-susceptible analog circuitry. These problems have been traditionally circumvented by circuit designers by isolating the analog and digital sections from one another.
One prior art solution involves the physical and/or mechanical separation of analog and digital sections. While certain circuits may be protected in this manner, however inelegant, such protection is at the expense of increased costs and the consumption of excess space. In some prior art circuit boards, analog and digital circuitry is disposed upon the same circuit board, however they are coupled together through expensive isolation amplifiers or optical coupling devices. While this approach allows construction of a hybrid circuit board, the expense and the distortion, noise and power consumption of isolation amplifiers and optical coupling devices are not very desirable. Moreover, in applications incorporating IC based analog-to-digital converters the analog and digital sections are inherently spanned and isolation impractical.
In some of these prior designs each of the analog and digital sections have had individual connections to earth ground. These multiple ground paths could potentially create a "ground loop" which would serve as a path for signals to flow from one ground to another, resulting in unwanted noise within the circuitry.
Some prior art hybrid circuit board designs may result in RF energy being injected through cabling connecting the hybrid circuit to an external circuit. In an audio signal apparatus the injection of noise into a connector cable will likely effect the signal source in two ways: noise current injection and radiative waves due to the "antenna effect" of the cable. The radiative interference will sometimes suppress a weak radio station and not allow a nearby tuner to receive the station signal. These effects result in interference and a poor quality signal, as RF noise injected and radiated to the signal source will return to the hybrid circuit as a noise which is processed along with the intended audio signal.
It is thus an object of the present invention to provide an electrical ground plane apparatus that allows the analog and digital sections to be directly coupled avoiding the need for isolation which, in turn, results in lower manufacturing costs and improved signal response.
It is an additional objection of the present invention to provide an electrical ground plane apparatus that omits ground loops and, thus, closes other paths for noise.
It is a further object of the present invention to prevent the injection of RF energy into circuitry external to the circuit board.
These and other objects of the present invention will become apparent in light of the present specification, claims and drawing.